Preparation of a magnetic core employed as a stator core of an electric motor or the like by pressure-forming soft magnetic powder is known in general. In this case, a high permeability can be easily obtained as compared with a case of preparing a magnetic core by superposing a plurality of electromagnetic steel plates. Further, the magnetic core can be integrally molded also when the same has a complicated structure.
In relation to a power magnetic core obtained by pressure-forming soft magnetic powder in this manner, Japanese Patent Laying-Open No. 10-335128, for example, discloses a power magnetic core aimed at implementing high magnetic flux density, low coercive force and low loss and having high mechanical strength and a method of manufacturing the same (Patent Document 1). On the other hand, Japanese Patent Laying-Open No. 2003-235186 discloses a method of manufacturing a magnetogenerator by circumferentially combining a plurality of generation coils with each other in order to attain downsizing (Patent Document 2).
Further, Japanese Patent Laying-Open No. 8-167518 discloses a high-frequency power magnetic core aimed at reducing hysteresis loss and further reducing iron loss and a method of manufacturing the same (Patent Document 3). The high-frequency power magnetic core disclosed in Patent Document 3 is prepared by compacting flattened shape-anisotropic soft magnetic powder in the form of a ring. At this time, the high-frequency power magnetic core is so prepared that the major axis direction of the shape-anisotropic soft magnetic powder is toward the radial direction of the ring on the assumption that the major axis of the shape-anisotropic soft magnetic powder is the hard axis of magnetization and the minor axis is the easy axis of magnetization.
In addition, Japanese Patent Laying-Open No. 11-238614 discloses a soft magnetic material aimed at having a high permeability and high saturation magnetic flux density as well as an excellent frequency characteristic and excellent mechanical strength and an electric apparatus employing the same (Patent Document 4). The stator of an electric motor disclosed in Patent Document 4 is prepared by pressure-forming magnetic powder composed of metal particles and metal oxides covering the metal particles.
Patent Document 1: Japanese Patent Laying-Open No. 10-335128
Patent Document 2: Japanese Patent Laying-Open No. 2003-235186
Patent Document 3: Japanese Patent Laying-Open No. 8-167518
Patent Document 4: Japanese Patent Laying-Open No. 11-238614